Technological advances, like surveillance planes and unmanned drones that scan thousands of square miles for smugglers; more aggressive tactics, like helicopter-borne Coast Guard snipers who can kill a smuggler's engines from above; and better intelligence gathering and sharing among an alphabet soup of government agencies.

"It's created a formidable force that has made it difficult for drug traffickers to do their work," said Adm. Thad W. Allen during a news conference Friday at Air Station Clearwater. "We have found in recent years that they have had to adapt to our tactics, rather than us having to adapt to theirs."

Yet by its own admission, the U.S. government stopped only a quarter of the illegal drugs headed for our shores in 2009 — and fell short of its own goal of choking off 40 percent of that supply.

Federal authorities estimated that drug interdiction efforts kept 175 tons of cocaine and 35 tons of marijuana from reaching the country in 2009. That's more than $5 billion worth of illegal drugs — but only 23 percent of what authorities estimated came across U.S. borders.

Authorities, though, could not specify how much illegal drugs were stopped on the way to Florida. But 44 percent of the drugs interdicted were from the Atlantic, including the Gulf of Mexico and the Caribbean Sea.

Allen also discussed how drug smuggling has evolved — from small airplanes to small boats — and where it's headed: underwater.

Smugglers are increasingly using self-propelled semisubmersible vehicles to transport drugs. They're not officially submarines, and can't completely dive underwater or travel as fast. But they can carry tons of illegal drugs while staying mostly hidden just below the waves, leaving little for radar to detect.

Their engines are also often armored to foil the Coast Guard sharpshooters who have become adept at disabling the faster, smaller boats still used by drug and human smugglers alike.

The threat was so significant, the admiral said, that lawmakers in the United States and Colombia outlawed the construction of such vessels. That's because smugglers caught moving drugs in them often scuttled the submersibles to destroy the evidence.

"The penalties are pretty much the same as if you were carrying narcotics," Allen said.

The job of finding all kinds of smugglers falls to the crews of the U.S. Customs and Border Protection's fleet of P-3 Orions, which use advanced sensors to search up to 200,000 square miles at a time.

Lothar Eckardt, the agency's director of air operations, said they're getting better at finding semisubmersibles. They found 11 last year, a new high for the United States, but smugglers are estimated to have dozens.

"Part of it has to stick out, like exhaust pipes for engines," he said, "and what sticks out can be picked out by radar."